The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A variety of intrusive and non-intrusive pressure sensing means are known for sensing pressure within an internal combustion engine cylinder when the engine is motoring and when the engine is firing.
Various aspects of internal combustion engine controls are known which rely on in-cylinder pressure measurements, particularly location of peak pressure (LPP), indicated mean effective pressure (IMEP) calibration and absolute peak pressure.
Known pressure ratio management (PRM) methods provide timing and cylinder charge control using constant property assumptions applicable to operating ranges of conventional spark ignited engines. The methods as relate to conventional spark ignited engines are based on constant property assumptions and computations of the ratio of fired to motored pressure during each engine cycle. From this, combustion timing can be estimated along with a parameter related to cylinder charge strength.
Compression-ignition engines and other engine control schemes operate over broad engine conditions, and effective control, including fuel control, fuel tailoring, charge ignition timing control, exhaust gas recirculation (EGR) control, is necessary to meet operator demands for performance and fuel economy and comply with emissions requirements. Furthermore, there is much variability, including that related to: components, e.g., fuel injectors; systems, e.g., fuel line and pressures; operating conditions, e.g., ambient pressures and temperatures; and, fuels, e.g., cetane number and alcohol content. The variability affects heat release and work output from individual cylinders, resulting in non-optimal performance of the engine. Any change in the engine performance is apparent in cylinder pressure ratios.
Referring now to FIG. 1, there is provided a graphical depiction of measured cylinder pressure ratio plotted based upon crank angle for varying operating conditions, specifically air/fuel ratios. The pressure ratio after expansion depends upon the work removed and heat loss of the engine. The graph indicates that engine operating conditions affect engine combustion and heat release, which can be indicated by a cylinder pressure ratio. The pressure ratio immediately after a heat release depends upon temperature and fuel/air equivalence ratio, phi, whereas the pressure ratio determined after expansion depends upon the work removed during expansion and heat loss through cylinder walls. An accurate and effective method to determine pressure ratio in an individual cylinder may be useable by an engine control system to improve engine control over a wide range of cylinder charge temperatures and compositions that can be found in operation of HCCI and diesel engines.
What is described herein comprises a method to monitor engine operation to determine engine heat release and combustion phasing, especially adapted for varying operating conditions that are related to compression ignition engines and homogeneous charge compression ignition (HCCI) engines having a wide range of cylinder charge temperatures and compositions.